[SECProto]

> but was struggling (am still) to see how it relates to a wooden trough that merely holds cables.

Overhead Catenary [1] is a standard term, for a system that has two wires overhead - one suspended from the posts (forming a series of catenary curve), the other suspended from that cable at regular intervals (and held level relative to the track). The wood in Boston's system seems to replace the catenary cable.

[1] https://en.wikipedia.org/wiki/Overhead_line#Overhead_catenar...